The importance of the sagittal position of the arm in the measurement of external rotation of the adducted shoulder

摘要

The measurement of external rotation of the shoulder is commonly performed in two ways: with the arm adducted or with the arm abducted to 90°. This measurement forms an important part of the assessment of shoulder function. It has been shown that the observer reliability of external rotation measurement is poor.1-4 Following the observation that the range of external rotation of the shoulder with the arm adducted altered depending on the exact position of the arm in the sagittal plane, we conducted a study to quantify the effect of a small increment of forward flexion (15°) on the range of external rotation. External rotation of the shoulder was measured in 40 asymptomatic shoulders and 20 'frozen' shoulders with the arm in a vertical position and in 15° of forward flexion. The range of external rotation decreased significantly in forward flexion in both groups. External rotation decreased by an average of 16.9° in the asymptomatic group and 13.5° in the frozen shoulder group. This study has shown that the sagittal position of the arm has an effect on the range of external rotation of the adducted shoulder. This may account for some of the observer variation in its measurement and affect the scores of certain outcome measures.